During a surgical procedure, and especially in procedures where the chest or abdomen is open, foreign objects such as surgical sponges, needles and instruments are sometimes misplaced within the patient's body cavity. In general any foreign object left within the body can cause complications, (i.e. infection, pain, mental stress), excepting objects such as clips and sutures that are purposely left as part of a surgical procedure.
Presently there are two surgically acceptable procedures for detection and removal of the foreign objects. Firstly, a count of all objects used in the operation is kept by surgical support staff. Secondly, x-ray detection is used to locate foreign objects.
It is not uncommon however, for object counts to be incorrect, because of human error, and the general chaos attendant with a surgical procedure. Furthermore, even x-ray detection is not flawless. Despite the fact that objects such as surgical sponges, (one of the most frequent objects left in the body), are embedded with an x-ray opaque material to make them more readily detectable, surgical sponges are often crushed into very small areas within a flesh cavity, whereby x-rays are not always able to sufficiently highlight them for detection. Furthermore, and most detrimentally, an x-ray is a time delayed detection method because of the requirement for film development (even with quick developing films). A patient will often be completely sutured closed before x-ray results are obtained, which may indicate the location of a foreign object within the patient. The detection delay, may therefore result in the necessity for the surgical team to re-open the patient, thereby increasing the morbidity of the operation.
The prior art is replete with means for the detection of foreign objects (aside from x-ray analysis) which may remain in body cavities following surgery. However, such means have either been prohibitively costly, involve detection devices which are too large to be meaningfully useful (i.e., they often impede utilization of the objects they are intended to locate) or simply do not provide effective detection.
There have been a number of devices described in numerous patents for detection of surgical objects such as surgical sponges, which operate by means of marker or tag systems using electromagnetic, magnetomechanical, electromechanical detection techniques. For example, U.S. Pat. No. 2,740,405, issued to Riordian, describes the use of a radioactive tracer for detection of the foreign objects. This method is however, among other things, subject to problems involving the hazards of storage and disposal of radioactive materials.
In another example of detection devices and methods, U.S. Pat. No. 3,422,816, issued to Robinson et al., teaches a technique wherein sponges are marked with a flexible plastic impregnated with paramagnetic or ferromagnetic powders which are detected by a metal detector. However, this method is limited by the small signals obtainable (making detection unreliable), and the lack of discrimination from other magnetically susceptible metal objects, such as surgical staples, which are intended to remain in the body.
In an improvement over the preceding patent, in U.S. Pat. No. 3,587,583, issued to Greenberg, sponges were marked with magnetized particles whose presence is detectable with magnetodiodes. Nevertheless, such method has also not proven to be practical or reliable.
A spate of patents disclose electronically based signal devices, such as disclosed in U.S. Pat. No. 4,114,601, issued to Ables, which discloses use of a gyromagnetic transponder for marking a sponge. Detection is accomplished by a mixing of two frequencies beating the tag. The method however appears impractical because of transmission loss at its operating frequency of 5 Ghz.
In theory, electronic locators should be ideal for the detection of surgical sponges. However, as a practical matter, it is difficult to make a small tag element with sufficient signal strength for reliable detection and at an economic cost. More importantly, the increased size of a tag element often results in a detrimental effect on the utilization of the object it is intended to locate. Thus, surgical sponges, the most common item for which detection is most important, are useful only if they can be deformed for use. However, deformation often distorts large tag elements and small tag elements do not provide sufficient signal strength for detection. A non-deformable large tag is totally counterproductive since it would effectively eliminate the usefulness of a sponge which must be deformed for use.
As an example of miniature electronic tags, U.S. Pat. No. 4,658,818, issued to Miller et al, discloses the use of a miniature electrical oscillator which is attached to each surgical implement and actuated at the time of surgery. Detection occurs by coupling the oscillation with the patient's tissue. However, because of interference considerations, this method does not appear to be practical.
In relatively recent U.S. Pat. No. 5,456,718, issued to Szymaitis, a marker is made of non-magnetostrictive or soft magnetic material which will emit known selected harmonic frequencies when exposed to alternating electromagnetic field. However, in practice, this creates a large non-deformable region within the sponge thereby interfering with its function.
In U.S. Pat. No. 5,105,829, issued to Fabian et al, a battery powered marker is disclosed which uses capacitive coupling of radio signal to tissue. However, for signal couple reasons the method is impractical.
In U.S. Pat. No. 5,190,059, Fabian et al teach a battery powered tag used in conjunction with a zone marker housing or field generator. Detection is effected as a result of characterizable field disturbance by the tag. The invention appears impractical since many surgeries would be obstructed by the addition of a zone housing.
In U.S. Pat. No. 5,057,095, Fabian et al teach marking surgical instruments with three types of resonant markers which produce identifying characteristics when exposed to an alternating magnetic field. First, there is a mangnetomechanical marker. Second, there is a magnetostrictive marker. (Both these devices are however susceptible to pressure and stress making them impractical in an environment, e.g., sponge, requiring compression, with pressure and stress as a function thereof.) Third, there is an electromagnetic LCR circuit. The markers described in the Fabian art are similar to security tags used in commercial retail anti-theft. As such they are susceptible to failure as they are deformed.
Surgical objects such as sponges must be deformable to conform to body cavity work area. If the tags are shrunk and encapsulated so that they would take up a sufficiently small deformation resistant area within a sponge, they could be used without impeding the function of the sponge. However, as the area of the described tags is shrunk, their coupling will decrease, making them almost invisible to a typical anti-theft system (to which the Fabian system is akin) and thus any detection system contemplated for their use in surgery.
Another very important characteristic absent from many of the prior art expedients is, besides being effective in use, the economics involved. Thus, many of the tags described in the prior art cost well in excess of two dollars per tag. While this is usually dwarfed by actual surgical costs, it is nevertheless a sufficiently significant amount to cause concern among potential users.